Constants library
342 values, each with its units, its uncertainty, and where it came from.
By category
Astronomical 107 values
Astronomical Unit, Light-Year, Parsec, and more
Chemistry 69 values
Avogadro constant, Atomic mass constant (unified atomic mass unit), Faraday constant, and more
Electromagnetic 31 values
Elementary charge, Electron charge-to-mass quotient, Vacuum magnetic permeability, and more
Engineering & Trade 71 values
Standard acceleration of gravity, Relative permittivity of air, Mains frequency (North America), and more
Equivalent Weight 10 values
Equivalent Weight of Sulfuric Acid, Equivalent Weight of Hydrochloric Acid, Equivalent Weight of Nitric Acid, and more
Fluid Properties 14 values
Density of Seawater, Density of Ice at 0 °C, Density of Mercury at 20 °C, and more
Material Properties 63 values
Relative permittivity of air, Relative permittivity of water, Relative permittivity of PTFE, and more
Mathematical 16 values
Pi, Tau (2π), Euler's Number, and more
Nuclear 16 values
Atomic mass constant energy equivalent, Electron mass energy equivalent, Proton mass, and more
Planets 55 values
Mass of Mars, Mean Radius of Mars, Surface Gravity of Mars, and more
Quantum 19 values
Planck constant, Reduced Planck constant (Dirac constant), Fine-structure constant, and more
Stars & Sun 21 values
Solar Mass, Nominal Solar Radius, Nominal Solar Luminosity, and more
Thermodynamic 37 values
Boltzmann constant, Molar gas constant, Stefan-Boltzmann constant, and more
Universal & Atomic 54 values
Speed of light in vacuum, Speed of light squared (mass-energy conversion factor), Planck constant, and more
Water Treatment 20 values
Ionic Product of Water (Kw at 25 °C), pKw of Water at 25 °C, Molar Mass of Calcium Carbonate, and more
All 342 constants, A to Z
- Absolute Roughness of Cast Iron Pipe
- Absolute Roughness of Commercial Steel Pipe
- Absolute Roughness of Drawn Tubing and Plastic Pipe
- Absolute zeroexact
- Acid Dissociation Constant of Acetic Acid
- Age of the Universe
- Alpha particle mass
- Apéry's Constantexact
- Astronomical Unitexact
- Atomic mass constant (unified atomic mass unit)
- Atomic mass constant energy equivalent
- Atomic Mass of Calcium
- Atomic Mass of Carbon
- Atomic Mass of Chlorine
- Atomic Mass of Hydrogen
- Atomic Mass of Iron
- Atomic Mass of Nitrogen
- Atomic Mass of Oxygen
- Atomic Mass of Sodium
- Atomic Mass of Sulfur
- Avogadro constantexact
- Axial Tilt of Mars
- Axial Tilt of Uranus
- Barn (nuclear cross-section unit)exact
- Base Dissociation Constant of Ammonia
- Bohr magneton
- Bohr radius
- Boiler horsepower
- Boltzmann constantexact
- British thermal unitexact
- Bulk Modulus of Water
- Calorie (thermochemical)exact
- Catalan's Constantexact
- Chandrasekhar Limit
- Characteristic impedance of vacuum
- Classical electron radius
- Common Logarithm of eexact
- Compressive Strength of Normal-Weight Concrete
- Compton wavelength of the electron
- Conductance quantumexact
- Cosmic Microwave Background Temperature
- Coulomb constant
- Critical Density of the Universe
- Cryoscopic Constant of Water
- Degrees per Radianexact
- Density of Aluminium Alloy 6061
- Density of Dry Air at 20 °C
- Density of Ice at 0 °C
- Density of Mercury at 20 °C
- Density of Reinforced Concrete
- Density of Seawater
- Density of Softwood Timber
- Density of Structural Steel
- Density of water at 20 °C
- Deuteron mass
- Distance to Alpha Centauri A
- Distance to Barnard's Star
- Distance to Betelgeuse
- Distance to Proxima Centauri
- Distance to Sirius
- Dynamic Viscosity of Air at 20 °C
- Dynamic Viscosity of Water at 20 °C
- Earth Axial Tilt (Obliquity of the Ecliptic)
- Earth Equatorial Radiusexact
- Earth Mean Orbital Speed
- Earth Mean Radius
- Earth Orbit Semi-Major Axis
- Earth Orbital Eccentricity
- Earth Polar Radiusexact
- Earth's magnetic field strength
- Ebullioscopic Constant of Water
- Electrical Resistivity of Aluminium at 20 °C
- Electrical Resistivity of Copper at 20 °C
- Electron charge-to-mass quotient
- Electron g-factor
- Electron gyromagnetic ratio
- Electron magnetic moment
- Electron mass
- Electron mass energy equivalent
- Electronvolt (in joules)exact
- Elementary chargeexact
- Equatorial Radius of Jupiter
- Equatorial Radius of Neptune
- Equatorial Radius of Saturn
- Equatorial Radius of Uranus
- Equivalent Weight of Caustic Soda
- Equivalent Weight of Citric Acid
- Equivalent Weight of Hydrated Lime
- Equivalent Weight of Hydrochloric Acid
- Equivalent Weight of Nitric Acid
- Equivalent Weight of Phosphoric Acid
- Equivalent Weight of Soda Ash
- Equivalent Weight of Sodium Bicarbonate
- Equivalent Weight of Sodium Bisulfate
- Equivalent Weight of Sulfuric Acid
- Escape Velocity of Jupiter
- Escape Velocity of Mars
- Escape Velocity of Mercury
- Escape Velocity of Neptune
- Escape Velocity of Saturn
- Escape Velocity of the Earth
- Escape Velocity of the Moon
- Escape Velocity of Uranus
- Escape Velocity of Venus
- Euler–Mascheroni Constantexact
- Euler's Numberexact
- Faraday constantexact
- Feigenbaum Deltaexact
- Fermi coupling constant
- Fine-structure constant
- First Dissociation Constant of Carbonic Acid
- First Dissociation Constant of Phosphoric Acid
- First pKₐ of Carbonic Acid
- First pKₐ of Phosphoric Acid
- First radiation constantexact
- Golden Ratioexact
- Gradians per Degreeexact
- Hartree energy
- Hazen-Williams C for Cast Iron Pipe
- Hazen-Williams C for Plastic Pipe
- Heat capacity ratio of air
- Heat capacity ratio of argon
- Heat capacity ratio of steam
- Hubble Constant
- Ice point (0 °C in kelvin)exact
- Inverse conductance quantumexact
- Inverse fine-structure constant
- Ionic Product of Water (Kw at 25 °C)
- Josephson constantexact
- Julian Yearexact
- Jupiter Orbit Semi-Major Axis
- Latent heat of fusion of water
- Latent heat of vaporisation of water
- Light-Yearexact
- Loschmidt constantexact
- Luminosity of Alpha Centauri A
- Luminosity of Sirius A
- Luminosity of Vega
- Magnetic flux quantumexact
- Mains frequency (Europe and most of the world)
- Mains frequency (North America)
- Manning's n for Concrete Channels
- Mars Orbit Semi-Major Axis
- Mass of Jupiter
- Mass of Mars
- Mass of Mercury
- Mass of Neptune
- Mass of Proxima Centauri
- Mass of Saturn
- Mass of Sirius A
- Mass of Sirius B
- Mass of the Earth
- Mass of the Moon
- Mass of Uranus
- Mass of Venus
- Maximum density of water (4 °C)
- Mean Earth–Moon Distance
- Mean Radius of Mars
- Mean Radius of Mercury
- Mean Radius of the Moon
- Mean Radius of Venus
- Mean Solar Dayexact
- Mechanical equivalent of heatexact
- Mercury Orbit Semi-Major Axis
- Molar gas constantexact
- Molar mass constant
- Molar Mass of Ammonia
- Molar Mass of Calcium Carbonate
- Molar Mass of Carbon Dioxide
- Molar Mass of Dinitrogen
- Molar Mass of Dioxygen
- Molar Mass of Glucose
- Molar Mass of Methane
- Molar Mass of Sodium Chloride
- Molar Mass of Sodium Hydroxide
- Molar Mass of Sulfuric Acid
- Molar Mass of Water
- Molar volume of an ideal gas at 0 °C and 1 atmexact
- Molar volume of an ideal gas at 25 °C and 1 atmexact
- Molar volume of an ideal gas at STP (0 °C, 100 kPa)exact
- Muon mass
- Muon-electron mass ratio
- Natural Logarithm of Tenexact
- Natural Logarithm of Twoexact
- Neptune Orbit Semi-Major Axis
- Neutron magnetic moment
- Neutron mass
- Neutron mass energy equivalent
- Neutron-proton mass ratio
- Newtonian constant of gravitation
- Nominal mains voltage (Europe)
- Nominal mains voltage (North America)
- Nominal Solar Luminosityexact
- Nominal Solar Radiusexact
- Normal boiling point of water
- Nuclear magneton
- Parsecexact
- Piexact
- pKₐ of Acetic Acid
- pKw of Water at 25 °C
- Planck constantexact
- Planck energy
- Planck length
- Planck mass
- Planck temperature
- Planck time
- Poisson's Ratio of Aluminium
- Poisson's Ratio of Concrete
- Poisson's Ratio of Steel
- Polar Radius of Jupiter
- Polar Radius of Neptune
- Polar Radius of Saturn
- Polar Radius of Uranus
- Proton charge-to-mass quotient
- Proton gyromagnetic ratio
- Proton gyromagnetic ratio over 2π
- Proton magnetic moment
- Proton mass
- Proton mass energy equivalent
- Proton rms charge radius
- Proton-electron mass ratio
- Quantum of circulation
- Radians per Degreeexact
- Radius of Betelgeuse
- Radius of Proxima Centauri
- Radius of Sirius A
- Radius of Sirius B
- Reduced Compton wavelength of the electron
- Reduced Planck constant (Dirac constant)exact
- Relative permittivity of air
- Relative permittivity of FR-4
- Relative permittivity of PTFE
- Relative permittivity of water
- Rydberg constant
- Rydberg energy (hcR∞)
- Sackur-Tetrode constant
- Saturn Orbit Semi-Major Axis
- Schwarzschild Radius of the Sun
- Second Dissociation Constant of Carbonic Acid
- Second Dissociation Constant of Phosphoric Acid
- Second pKₐ of Carbonic Acid
- Second pKₐ of Phosphoric Acid
- Second radiation constantexact
- Shear Modulus of Aluminium Alloy
- Shear Modulus of Structural Steel
- Sidereal Day
- Sidereal Orbital Period of Jupiter
- Sidereal Orbital Period of Mars
- Sidereal Orbital Period of Mercury
- Sidereal Orbital Period of Neptune
- Sidereal Orbital Period of Saturn
- Sidereal Orbital Period of the Moon
- Sidereal Orbital Period of Uranus
- Sidereal Orbital Period of Venus
- Sidereal Rotation Period of Jupiter
- Sidereal Rotation Period of Mars
- Sidereal Rotation Period of Mercury
- Sidereal Rotation Period of Neptune
- Sidereal Rotation Period of Saturn
- Sidereal Rotation Period of Uranus
- Sidereal Rotation Period of Venus
- Sidereal Year
- Solar Constant (Total Solar Irradiance)
- Solar Effective Temperatureexact
- Solar Mass
- Solar Wind Speed (typical)
- Solubility Product of Calcium Carbonate
- Solubility Product of Calcium Sulfate
- Specific gas constant for dry air
- Specific gas constant for water vapour
- Specific Gravity of Soil Solids
- Specific heat capacity of dry air
- Specific heat capacity of ice
- Specific heat capacity of liquid water
- Specific Heat of 30 % Propylene Glycol
- Speed of light in glass
- Speed of light in vacuumexact
- Speed of light in water
- Speed of light squared (mass-energy conversion factor)exact
- Speed of Sound in Dry Air at 20 °C
- Speed of Sound in Steel
- Speed of Sound in Water at 20 °C
- Square Root of Threeexact
- Square Root of Twoexact
- Standard acceleration of gravityexact
- Standard atmosphereexact
- Standard Gravitational Parameter of the Earth
- Standard Gravitational Parameter of the Sun
- Standard Hydrogen Electrode Potentialexact
- Standard Potential of the Copper Half-Cell
- Standard Potential of the Ferric–Ferrous Couple
- Standard Potential of the Oxygen–Water Couple
- Standard Potential of the Silver Half-Cell
- Standard Potential of the Zinc Half-Cell
- Standard state pressureexact
- Stefan-Boltzmann constantexact
- Surface Gravity of Jupiter
- Surface Gravity of Mars
- Surface Gravity of Mercury
- Surface Gravity of Neptune
- Surface Gravity of Saturn
- Surface Gravity of the Moon
- Surface Gravity of Uranus
- Surface Gravity of Venus
- Tau (2π)exact
- Tau lepton mass
- Temperature Coefficient of Resistance, Copper
- Thermal Conductivity of Air
- Thermal Conductivity of Aluminium
- Thermal Conductivity of Copper
- Thermal Conductivity of Fibreglass Batt Insulation
- Thermal Conductivity of Rigid Foam Board
- Thermal Conductivity of Type 304 Stainless Steel
- Thermal Conductivity of Water
- Thermal Expansion Coefficient of Aluminium
- Thermal Expansion Coefficient of Carbon Steel
- Thermal Expansion Coefficient of Concrete
- Thermal Expansion Coefficient of Copper
- Thermal Expansion Coefficient of PVC
- Thermal Expansion Coefficient of Type 304 Stainless
- Third Dissociation Constant of Phosphoric Acid
- Third pKₐ of Phosphoric Acid
- Thomson cross section
- Ton of refrigerationexact
- Triple point of water
- Triple point pressure of water
- Tropical Year
- Uranus Orbit Semi-Major Axis
- Vacuum electric permittivity
- Vacuum magnetic permeability
- Vapour Pressure of Water at 20 °C
- Venus Orbit Semi-Major Axis
- von Klitzing constantexact
- Wien displacement law constant (frequency)exact
- Wien displacement law constant (wavelength)exact
- Yield Strength of 6061-T6 Aluminium
- Yield Strength of ASTM A36 Steel
- Yield Strength of ASTM A992 Steel
- Young's Modulus of Aluminium Alloy 6061
- Young's Modulus of Normal-Weight Concrete
- Young's Modulus of Structural Steel
- Young's Modulus of Type 304 Stainless Steel